Among a multitude of different battery types, there exist so-called film batteries. Those batteries are composed of thin materials with thickness in the range of micrometers, allowing a total battery thickness in the range of 1 mm or less. So they may exhibit small dimensions and are therefore applicable to a large spectrum of different applications. Generally, such batteries or electrochemical cells can be formed into any arbitrary shape. They can be stacked, used in parallel and generally provide a comparatively large energy density.
Film electrochemical cells may also provide a particular mechanical flexibility. Hence, they are typically bendable and elastically deformable to a certain degree. This property is of prime importance for reliable portable products subject to mechanical stress, like smart cards, etc . . . .
Electrochemical cells typically comprise an anode, an anode current collector, a cathode, a cathode current collector, a separator extending between anode and cathode and an electrolyte. Moreover and in order to provide a desired mechanical flexibility, anode and cathode current collectors have to provide corresponding flexible properties. Since the current collectors are typically arranged at the outside facing portions of anode and cathode, they may become particularly subject to mechanical stress when the electrochemical cell is bent.
In practical applications and in particular after a number of bending or folding operations, e.g. after about 100 or 500 bending operations, conventional current collectors may exhibit a fissured structure or may even tend to show damaged portions at least on their surface. Such current collectors typically formed on the basis of metal foils therefore tend to deteriorate in response to repeated bending operations.
Additionally, conventional electrochemical cells always comprise a housing or an encapsulation, e.g. a polymer/aluminum/polymer laminate to receive and to enclose the assembly of anode current collector, anode, separator, electrolyte, cathode and cathode current collector. For contacting the current collectors with connector tabs extending through the housing, a rather elaborate mutual interconnection of current collectors and connector tabs must be provided. Additionally, the connector tabs have to be passed through the encapsulation or housing, e.g. by means of polymeric sleeves. The interconnection of connector tabs with current collectors is rather space consuming and limits the spatial energy density of the electrochemical cell.
It is therefore an object of the present invention to provide an improved electrochemical cell with an increased volumic energy density. In another object, the invention should provide a flexible electrochemical cell being less prone and less sensitive to repeated bending or folding operations. Moreover, the internal structure of the electrochemical cell should be rather simple, space saving and their production should be cost efficient.